This invention relates to a process of producing carbon monoxide from light hydrocarbons having an average C number of not more than 15 by a catalytic cracking with water vapor in two cracking stages, followed by a separation of carbon monoxide from the product gas.
It is already known to produce carbon monoxide by a steam reforming process in which a feedstock such as natural gas, refinery gas, liquefied gas or naphtha is treated with water vapor at elevated temperatures in contact with a nickel catayst and is thus converted to a gas which is rich in hydrogen and carbon monoxide. When the product gas has been cooled down, the carbon dioxide and water vapor still contained therein are removed and the purified gas is decomposed at low temperature.
It is also known to improve the yield of carbon monoxide in that the carbon dioxide which has been scrubbed off is recycled to the cracking process (Printed Ger. application No. 1,913,657).
This recycling of the carbon dioxide imposes higher requirements as regards the materials of the equipment and the catalysts used in said process. The carbon dioxide which is obtained is saturated with water vapor and can be recycled only if a multistage recycling compressor is provided which has suitable interstage coolers of corrosion-resisting material. Besides, the catalytic cracking is performed in a tubular heater, in which the cracking conditions and the catalyst must be selected so as to prevent a deposition of carbon on the catalyst. Where a difficult feedstock, such as naphtha, is used, the direct conversion of the naphtha in a tubular heater in the presence of recycled carbon dioxide imposes extreme requirements as regards the catalysts which can be employed, and a large surplus of water vapor must be employed although this lowers the productivity.
Another disadvantage of the recycling of CO.sub.2 is significant in practice and resides in the fact that the automatic control of the entire plant is more complicated because the carbon monoxide must be controlled too.